DEFORMATION INDUCED MARTENSITIC TRANSFORMATIONS IN CR-MN AUSTENITIC STEELS
Austenitic steels based on the Fe-Cr-Mn system commonly exhibit martensitic transformations in the sequence gamma, epsilon, alpha. The occurrence of the intermediate h.c.p. epsilon phase, although not unknown in Fe-Cr-Ni alloys, is characteristic of austenites having a significant content of manganese. Since this element has a stabilizing effect only about half that of nickel, increased amounts of carbon and/or nitrogen are therefore required to produce a fully austenitic structure. Stacking fault energy is reduced as a result of the negative influences of manganese and, possibly nitrogen. This favours the gamma, epsilon transformation, which is crystallographically equivalent to the introduction of intrinsic stacking faults on alternate close packed planes. Subsequent epsilon, alpha transformation, by secondary shear, corresponds to the well-established Nishiyama-Wassermann or Kurdjumov-Sachs orientation relationships. Experimental work was performed on 10Cr18Mn steels of differing carbon and nitrogen contents. These materials were completely austenitic at room temperature and remained so on quenching in liquid nitrogen. Martensitic transformation was produced, however, by deformation at room temperature. The Md temperature was approximately 100"rm o"C for both the martensitic phases. Annealing experiments indicated that reversion of epsilon martensite to austenite took place in the temperature range 200-400"rm o"C and reversion of alpha was complete at around 600"rm o"C. Microstructural investigations were carried out by scanning and transmission electron microscopy, X-ray diffraction, magnetic measurements, density measurements and indentation hardness tests. Quantitative estimates were thence made of the extent of transformation and its contribution to the stress-strain behaviour of the steels.
Bibliographic Reference: PHASE TRANSFORMATIONS '87, UNIVERSITY OF CAMBRIDGE/UK, JULY 6-10, 1987, AVAILABILITY: CEC-LUXEMBOURG, DG XIII/A2, BP 1907, MENTIONING PAPER ORA 33113 E
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Record Number: 1989126073000 / Last updated on: 1989-05-01
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